The human face is an important and complex communication channel. Humans can, however, easily read in a face not only identity information but also facial expressions with high accuracy. Here, we present the results of four psychophysical experiments in which we systematically manipulated certain facial areas in video sequences of nine conversational expressions to investigate recognition performance and its dependency on the motions of different facial parts. The results help to demonstrate what information is perceptually necessary and sufficient to recognize the different facial expressions. Subsequent analyses of the facial movements and correlation with recognition performance show that, for some expressions, one individual facial region can represent the whole expression. In other cases, the interaction of more than one facial area is needed to clarify the expression. The full set of results is used to develop a systematic description of the roles of different facial parts in the visual perception of conversational facial expressions.